The lung has and will always remain one of the most important organs in the human body. Lungs play a crucial role in allowing the body to let in oxygen and let out carbon dioxide. How would a human function without their lungs? Melissa Benoit, a 32 year old from Canada, was dying from a severe lung infection, that initiated organ failure and had an effect on the digestive system. The lung infection was a result of a super-bacteria, that was resistant to most antibiotics, and was able to spread the disease (cystic fibrosis), throughout her body. In what is the world’s first procedure, doctors removed her lungs entirely. Despite being so close to death, Melissa managed to survive due to a transplant that was made in time, however what is most astonishing, is that for 6 days, she survived without lungs. During this time she was placed on an incredibly sophisticated life support machine, which helped her heart pump blood. Two devices were connected to her heart, oxygenating her blood and removing carbon dioxide, whilst another device helped circulate the oxygen-rich blood throughout her body.
The trachea is the main airway from the nose down into the chest, it is a wide tube supported by incomplete rings of strong,and flexible c-shaped cartilage, which stop the trachea from collapsing. Within these trachea, and its branches, are lines of ciliated epithelium, with goblet cells between and below the epithelial cells. The goblet cell secrete mucus onto the lining of the trachea, to trap dust and microorganisms that have escaped the nose lining. The cilia beat and move the mucus away from the lungs, moving away trapped dirt and microorganisms. When cigarettes are smoked, than the cilia stops beating, causes the “smokers cough”. The trachea divides to form the left bronchi, which leads to the left lung, and the right bronchus that leads to the right lung. They are smaller structures of the trachea. The bronchioles divide to form many small bronchioles, which have no cartilage rings, and are of a diameter 1mm or less. The walls of the bronchioles are of smooth muscle, when this muscle contracts, the bronchioles close up. When the smooth muscle relaxes, the bronchioles dilate. This alters the amount of air that reach the lungs. Bronchioles are lined with a thin layer of flattened epithelium, which allows for gas exchange.
The alveoli carry out the most important aspects of gas exchange, the alveoli are tiny air sacs and are unique to mammalian lungs. They are extremely small and consist of a layer thin, flattened epithelial cells, along with some collagen and elastic fibres (elastin). These elastic tissues allow the alveoli to stretch as air is drawn in, and they help squeeze air out when they return to their resting size. This is the function of elastic recoil. The alveoli are efficient for gaseous exchange due to their large surface area, thin layers, good supply of blood; to maintain a steep concentration gradient. Along with good ventilation, through steep diffusion gradients for oxygen and carbon dioxide between the blood and the air in the lungs. The inner surface of the alveoli contain a lung surfactant, which allows for the alveoli to remain inflated.
Air is moved in and out of the lungs, by pressure changes in the chest cavity. The diaphragm is a broad and domed sheet of muscle that forms the floor of the thorax. When you take air in, energy is used, as the diaphragm contracts, and flattens. The external intercostal muscles contract, and move the ribs upwards and outwards, the volume of the thorax increases, and the pressure in the thorax is reduced. Air is drawn in through the nasal passage. When air is exhaled, the muscles relax due to it being a passive process. The diaphragm relaxes, and the external intercostal muscles relax so the ribs move down and inwards under gravity. The elastic fibres in the alveoli of the lung return to their normal length. This process decreases the volume of the thorax.
The lungs play a role, and a role that is incredibly complex and requires multiple processes to be carried out alongside, in order to maintain pressure. Lungs are taken for granted, not many realise what an important role it has in doing something as simple (to us) as breathing.